The following documents, mentioned in the description hereafter, illustrate the state of the art:                Barnola, A. S., Andrieux B., Tonellot T., Voutay O., 2003, Pre-stack stratigraphic inversion and attribute analysis for optimal reservoir characterization, 73rd Ann. Internat. Mtg: Soc. of Expl. Geophys., 1493-1496, Dallas.        Bertrand, C., Tonellot T., Fournier F., 2003, Seismic facies analysis applied to P and S impedances from pre-stack inversion, 72nd Ann. Internat. Mtg: Soc. of Expl. Geophys., 217,220.        Bourbié, T., Coussy, O., Zinszner, B., 1987, Acoustics of porous media, Editions Technip, Paris.        Brac J. P. et al., 1988, Inversion with A Priori Information: An Approach to Integrated Stratigraphic Interpretation, Reservoir Geophysics R.E. Sheriff ed. Investigation in Geophysics, 7, SEG, Tulsa.        T. Tonellot, D. Macé, V. Richard, 1999, Prestack elastic waveform inversion using a priori information, 69th Ann. Internat. Mtg: Soc. of Expl. Geophys., paper 0231, p. 800-804.        Eberhart-Phillips, D., Han, D.-H., and Zoback, M. D., 1989, Empirical relationships among seismic velocity, effective pressure, porosity, and clay content in sandstone: Geophysics, 54, 82-89.        Grauls, D., Dunand, J. P., Beaufort, D., 1995, Predicting abnormal pressure from 2D seismic velocity modeling: Offshore Technology Conference, paper OTC 7692.        Harkins, K. L., Baugher, J. W., 1969, Geological significance of abnormal formation pressures: J. Petroleum Geol., 961-966        Lucet, N., Déquirez, P.-Y. and Cailly, F., 2000, Well to seismic calibration: A multiwell analysis to extract one single wavelet, 70th Ann. Internat. Mtg: Soc. of Expl. Geophys., 1615-1618.        Pennebecker, E. S., 1968, Seismic data indicate depth, magnitude of abnormal pressure: World oil, 166, 73-78        Reynolds, E. B, 1970, Predicting overpressured zones with seismic data: World oil, 171, 78-82.        Shapiro, S. A., 2003, Elastic piezosensitivity of porous and fractured rocks: Geophysics, 68, 482-486.        Tonellot, T., Macé, D. and Richard, V., 2001, Joint stratigraphic inversion of angle-limited stacks, 71st Ann. Internat. Mtg: Soc. of Expl. Geophys., 227-230.        Voutay, O., Fournier, F. and Royer, J., 2002, Seismic interpretation with new attributes extracted from a prestack multicube analysis, 72nd Ann. Internat. Mtg: Soc. of Expl. Geophys., 1762-1765.        Yilmaz, O., 1987, Seismic Data Processing: Soc. of Expl. Geophys., 526. Zimmerman, R. W., 1984, The effect of pore structure on the pore and bulk compressibility of consolidated sandstones: Ph.D. dissertation, University of California at Berkeley.        
The presence of overpressure zones under exploration can have serious financial and sometimes human consequences during drilling if the fluid pressures are not known. Prediction of the presence of overpressure zones and, more generally, quantitative evaluation of these overpressures has become a priority for oil companies. In fact, in the sphere of exploration, the fluid pressure can be close to the minimum principal stress and induce the re-opening of fractures or possibly initiate hydraulic fracturing. In the sphere of drilling, it is important to know the pressure difference between the fluid pressure and the minimum stress in place for the design of well casings, and to predict the mud weight so as to prevent blowouts in underbalanced drilling or drilling mud losses in overbalanced drilling. Finally, depletion in overpressure zones can induce notable stress redistributions, possibly with great consequences on the productivity of reservoirs. Thus, a good quantitative evaluation of the fluid pressures and of their connections with the stress variations is also important in the sphere of production.
There are many methods allowing quantitative evaluation of fluid pressures from physical measurements (and not from modeling): formation tests, drill bit drilling rate, clay density measurements, gas shows, fluid flow rate measurements, wireline logging, etc. Among these methods, the geophysical methods, and more particularly the seismic methods, having a higher spatial resolution than their competitors (gravimetry for example) are the only ones allowing this at a distance from wells. It is therefore essential to best exploit the seismic data.
However, the conventionally used seismic processings of velocity analysis type (Yilmaz, 1987) have a limited efficiency (Pennebaker, 1968, Grauls et al., 1995), mainly because, on the one hand, of their spatial resolution, too weak to be efficiently used for drilling and, on the other hand, because they do not take sufficiently into account the lithologic variations (Reynolds, 1970), often critical in overpressure phenomena. In order to understand these main technical problems, the conventional procedure for quantitative evaluation of overpressures from seismic data is summarily described. The various stages are as follows:                obtaining a seismic velocity model that is as precise as possible, through fine velocity analysis,        deducing a reference compaction curve (seismic velocity as a function of depth) referred to as “normal compaction” curve (corresponding to the hydrostatic distribution of the fluid pressure),        interpreting the differences between the compaction curve measured with the seismic method and the normal compaction curve in terms of fluid pressure anomalies. The anomalies (or deviations in relation to the hydrostatic distribution) can be positive (overpressures) or negative.        
The main problems of these methods are, on the one hand, the relatively low spatial resolution of the conventional methods that make them difficult to use for drilling operations. The second problem is the implicit assumption according to which any anomalic velocity change is attributed to an overpressure, while dismissing for example causes such as the lithology change (Reynolds, 1970, for example). Lithologic verification is performed a posteriori in the conventional method. In other words, one checks after all the processings that the pressure anomalies are not due to a lithologic variation.
The method provided, based on pre-stack inversion of seismic data, allows these two major drawbacks to be overcome by providing a fluid pressure cube at a sufficiently precise scale for the drill man while taking into account the lithology explicitly in the processing.